Essentially all rubbers are susceptible to deterioration as a result of prolonged exposure to aging in an oxygen atmosphere, especially at elevated temperature. A great deal of effort has been spent and many antioxidant compositions have been suggested for use in reducing the degradative effects of oxygen on these materials. However, many of the compositions which heretofore have been suggested as antioxidants for these materials have not provided the desired long term stabilization due possibly to the tendency of many of the commercially available stabilizers to volatilize when the polymeric products are exposed to elevated temperatures over prolonged periods of time.
Nitrile rubbers normally are used when materials are required with superior resistance to oil and hydrocarbons, good heat stability, abrasion resistance and low permanent set. Therefore, in the normal use of nitrile rubbers, the loss of antioxidants by extraction and/or volatilization is expected but not desirable. Since nitrile rubbers are used widely in automotive and related industries where operating temperatures have risen gradually, the service life of such rubber parts has been affected, and a demand for higher temperature resistant and stable nitrile rubber has resulted.